NOAA Natural and Weather Events (tornadoes, flash floods, avalanches, blizzards, forest fires, hurricanes, tsunamis, volcanic eruptions and earthquakes), State and County Emergency Alerts (non-weather civil emergencies such as localized chemical spills, nuclear power plant emergenvies, gas line breaks, checmical storage center emergencies, train derailments, oil refinery fires, immediate evacuations, shelter-in-place, and missing children alerts. And of course, the paranoid heart of the matter: National Emergencies such as national attack warnings, terrorist attaalerts, bio-warfare alerts, and other immediate life-threatening emergencies.
Okay: I was in New York on 9/11. Didn't have AlertGuard (and in fact had to be alerted by a friend from out of town who called to ask me if I was okay...I, clueless as usual, had no idea what was happening). But I have to say that, once alerted, I got more information than I needed, all day, on every channel except for Nickelodeon (which very usefully showed cartoons all day, for those of us who have kids and didn't want them watching and rewatching the news coverage). But there are already many systems in place for contacting the citizenry and letting them know what's happening. And if you're not watching your television (say, you're at work or asleep or out in the back yard or at the mall) you're not going to be able to avail yourself of the service provided by AlertGuard.
I am not in the market for a new TV, but I have to say I would pay good money -not- to have AlertGuard on my set; I really resent the fact that manufacturers are using the anxiety of the times to make money. It may be inevitable, but I still hate it a lot.